x=18l/2l=9 which means the pressure is 9 times greater after the volume is down to 2l. To find the final pressure, we can use P(1)=xP(0), when we add the numbers in, it looks like this: P(1)=9*42 kPa=378 kPa
if the concentration of products is decreased, the equilibrium will shift toward the products). add an inert gas (one that is not involved in the reaction) to the constant-volume reaction mixture: this will increase the total pressure of the system, but will have no effect on the equilibrium condition.
i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)